Patent application DE 41 34 461 A1 shows a method for avoiding excessive currents in a welding converter that generates a two-phase pulse-width-modulated alternating current from a rectified AC line current using power semiconductors, which generated current is supplied to the primary side of a welding transformer.
The method comprises the following steps: The current of at least one phase of the primary circuit is measured via a sensor, the time derivative of each measured current signal is formed via differentiation with respect to time, the time-derived measurement signal is compared to a specified maximum value. If the time-mapped measurement signal exceeds the specified maximum value, a signal is emitted that leads to the deactivation of the power semiconductors.
The arrangement shown here comprises a so-called B6-input bridge that is connected directly to a multiphase power grid. Such input bridges cause extremely high harmonic currents in the power grid. In particular, the fifth harmonic can be up to 80%, and even if a line inductor is connected upstream, a maximum reduction of 40% can be expected.
The object of the disclosure is to provide an apparatus and a method so that the above-mentioned disadvantageous effects are avoided or minimized as much as possible.